You asked about Button Focus.
@ewpatton provided this answer a while ago on the forum(paraphrased):
The original use of the GotFocus/LostFocus events were when Android phones had trackballs to navigate the UI. Focus would move when you moved the trackball highlight over a component (e.g., button). In the days of touch screens and no trackballs, the events still exist but are likely only triggered in limited circumstances (using tab key in an emulator being one, accessibility focus is another).